The present invention relates generally to ion implantation systems, and more specifically to a gas delivery system and method for supplying gas across a voltage gap in an ion implantation system or other type equipment.
Ion implanters are used to implant or xe2x80x9cdopexe2x80x9d silicon wafers with impurities to produce n or p type extrinsic materials. The n and p type extrinsic materials are utilized in the production of semiconductor integrated circuits. As its name implies, the ion implanter dopes the silicon wafers with a selected ion species to produce the desired extrinsic material. Implanting ions generated from source materials such as antimony, arsenic or phosphorus results in n type extrinsic material wafers. If p type extrinsic material wafers are desired, ions generated with source materials such as boron, gallium or indium will be implanted.
The ion implanter includes an ion source for generating positively charged ions from ionizable source materials. The generated ions are formed into a beam and accelerated along a predetermined beam path to an implantation station. The ion implanter includes beam forming and shaping structure extending between the ion source and the implantation station. The beam forming and shaping structure maintains the ion beam and bounds an elongated interior cavity or region through which the beam passes en route to the implantation station. When operating the implanter, the interior region must be evacuated to reduce the probability of ions being deflected from the predetermined beam path as a result of collisions with air molecules.
For high current ion implanters, the wafers at the implantation station are mounted on a surface of a rotating support. As the support rotates, the wafers pass through the ion beam. Ions traveling along the beam path collide with and are implanted in the rotating wafers. A robotic arm withdraws wafers to be treated from a wafer cassette and positions the wafers on the wafer support surface. After treatment, the robotic arm removes the wafers from the wafer support surface and redeposits the treated wafers in the wafer cassette.
FIG. 1 depicts an exemplary ion implanter, shown generally at 10, which includes an ion source 12 for emitting ions that form an ion beam 14 and an implantation station 16. Control electronics 11 are provided for monitoring and controlling the ion dosage received by the wafers within a process chamber 17 at the implantation station 16. The ion beam 14 traverses the distance between the ion source 12 and the implantation station 16.
The ion source 12 includes a plasma chamber 18 defining an interior region into which source materials are injected. The source materials may include an ionizable gas or vaporized source material. Source material in solid form may be deposited into a pair of vaporizers 19. Alternatively, gas sources stored either in high pressure or low pressure type containers may be used. The gaseous hydrides arsine (AsH3) and phosphine (PH3) are used commonly as sources of arsenic (As) and phosphorous (P) in ion implantation. Due to their toxicity, such gaseous sources are often maintained local to the ion source 12 in low pressure SDS (safe delivery system) bottles.
The source material is injected into the plasma chamber and energy is applied to the source materials to generate charged ions in the plasma chamber 18. The charged ions exit the plasma chamber interior through an elliptical arc slit in a cover plate 20 overlying an open side of the plasma chamber 18.
The ion beam 14 travels through an evacuated path from the ion source 12 to the implantation station 17, which is also evacuated via, for example, vacuum pumps 21. Ions in the plasma chamber 18 are extracted through the arc slit in the plasma chamber cover plate 20 and are accelerated toward a mass analyzing magnet 22 by a set of electrodes 24 adjacent the plasma chamber cover plate 20. Ions that make up the ion beam 14 move from the ion source 12 into a magnetic field set up by the mass analyzing magnet 22. The mass analyzing magnet is part of the ion beam forming and shaping structure 13 and is supported within a magnet housing 32. The strength of the magnetic field is controlled by the control electronics 11 by adjusting a current through the magnet""s field windings. The mass analyzing magnet 22 causes the ions traveling along the ion beam 14 to move in a curved trajectory. Only those ions having an appropriate atomic mass reach the ion implantation station 16. Along the ion beam travel path from the mass analyzing magnet 22 to the implantation station 16, the ion beam 14 is further shaped, evaluated and accelerated due to the potential drop from the high voltage of the mass analyzing magnet housing 32 to the grounded implantation chamber.
The ion beam forming and shaping structure 13 further includes a quadrupole assembly 40, a moveable Faraday cup 42 and an ion beam neutralization apparatus 44. The quadrupole assembly 40 includes set of magnets 46 oriented around the ion beam 14 which are selectively energized by the control electronics (not shown) to adjust the height of the ion beam 14. The quadrupole assembly 40 is supported within a housing 50.
Coupled to an end of the quadrupole assembly 40 facing the Faraday flag 42 is an ion beam resolving plate 52. The resolving plate 52 includes an elongated aperture 56 through which the ions in the ion beam 14 pass as they exit the quadrupole assembly 40. The resolving plate 52 also includes four counterbored holes 58. Screws (not shown) fasten the resolving plate 52 to the quadrupole assembly 40. At the resolving plate 52 the ion beam dispersion, as defined by the width of the envelope Dxe2x80x2, Dxe2x80x3, is at its minimum value, that is, the width of Dxe2x80x2, Dxe2x80x3 is at a minimum where the ion beam 14 passes through the resolving plate aperture 56.
The resolving plate 52 functions in conjunction with the mass analyzing magnet 22 to eliminate undesirable ion species from the ion beam 14. The quadrupole assembly 40 is supported by a support bracket 60 and a support plate 62. The support bracket 60 is coupled to an interior surface of the resolving housing 50.
As stated supra, ion source materials are provided to the ion source 12 in a variety of different ways. Because switching solid source materials is a relatively time-consuming process, use of gaseous source materials is often utilized. Since some of the gaseous ion source materials are toxic, SDS bottles are often utilized which are not pressurized to enhance safety in the event of leakage. Such containers typically are stored in a gas box which is local to or integrated into the ion implanter. Consequently, replacement of the SDS bottles for purposes of ion source material replenishment requires entry into the clean room in which the ion implanter resides, which contributes to machine down time and potential particulate contamination. Therefore it would be desirable to further improve upon present ion source delivery systems.
The present invention is directed to a gas delivery system for an ion implanter in which a gaseous ion source material is electrically isolated and/or located remote from the ion implanter. The ion source material may reside at a location remote from the ion implanter such as a centralized gas bunker and is maintained at a first voltage potential such as a ground potential. The gaseous ion source material is then delivered to the ion source of the ion implanter which resides at a second potential via a gas delivery network and is coupled to the implanter via an electrically insulative connector. The connector serves as a voltage isolator between the gas storage and/or delivery network provided at the first voltage potential and the ion source of the ion implanter which operates at the second potential.
The gas delivery system of the present invention provide various advantages over prior art gas delivery systems. For example, because the gaseous ion source is stored and transferred from a remote location, for example, in the gas bunker, the downtime associated with ion source material changes is reduced substantially. Further because ion source material replacements may be effectuated remote from the implanter, the potential particulate contamination due to handling gas bottles in the clean room is eliminated. In addition, since the gas box which is local to the ion implanter no longer holds individual gas bottles (e.g., SDS bottles), the size of the gas box may be reduced significantly.
According to one aspect of the present invention, a gas delivery system is disclosed which comprises a gas source at a first voltage potential and an ion source at a second voltage potential which is greater than the first potential. The gas delivery system further comprises an electrically insulative connector coupled between the gas source and the ion source which facilitates a fluid connection between the gas source and the ion source and electrically isolates the first potential from the second potential.
According to another aspect of the present invention, a gas delivery high voltage isolator structure is disclosed. The isolator structure comprises a first electrically insulative tube surrounded by a second electrically insulative tube in telescope arrangement. The isolator structure is terminated at each end with an adapter, for example, a stainless steel adapter and coupled, for example, by welding, to a VCR-type fitting. The first tube carries the gaseous ion source material at a first pressure and a spacing between the first and second tube carries an inert barrier gas at a second pressure which is different (e.g., higher) than the first pressure. The isolator structure may further include a monitoring port associated therewith, wherein the second pressure may be monitored and used to identify leakage associated with the isolator structure. The isolator structure may further exhibit a length sufficient to prevent arcing between each end, wherein the ends exhibit a potential difference thereacross.
According to yet another aspect of the present invention, a method of delivering gas to an ion implantation system is disclosed. The method comprises maintaining a source gas at a storage location at a first voltage potential which is less than a second voltage potential at the ion source of the ion implantation system. The method further comprises delivering the source from the storage location to the ion source. The delivery is accomplished, for example, by coupling a high voltage isolator structure between a bulk gas delivery system and the ion source. The bulk gas delivery system is maintained at the first potential, for example, circuit ground while the ion source is maintained at the second voltage potential, for example, 80 KV. The isolator structure allows for the storage and replacement of ion source materials remote from the implantation system, thereby facilitating easy replacement and changeover of ion source material.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.